procedure TForm1.Button1Click(Sender: TObject);
var 
  Fl, iFileLength, iBytesReadб i: Integer;
  st: PChar;
begin
  fl:=FileOPen('c:\1.txt',fmOpenRead);
  iFileLength := FileSeek(fl, 0 , 2 );
  st := PChar(AllocMem( 10 ));
  FileSeek(fl, 0 , 0 );
// Читаем  10  букв 
  iBytesRead := FileRead(fl, st^,  10 );
  memo1.Lines.Add(st);
// Сдвигаемся и читаем еще  10  букв 
  FileSeek(fl, 100 , 0 );
  iBytesRead := FileRead(fl, st^,  10 );
  memo1.Lines.Add(st);
  FileClose(fl);
  FreeMem(st);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  iFileLength, i: Integer;
  st: PChar;
  FS: TFileStream;
begin
  Memo1.Clear;
  FS:= TFileStream.Create('c:\1.txt', fmShareDenyNone);
  iFileLength := FS.Size;
  st := PChar(AllocMem(iFileLength+ 1 ));
  FS.Read(st^, iFileLength);
  FS.Free;
  Memo1.Lines.Add(st);
  FreeMem(st);
end;